How much credit do you really have?

One expert advises keeping balances to 10 percent or less of the limit.

Your utilization rate isn't the only factor you want to consider.

When you apply for a loan, lenders will look at your debt load.

For some spenders, a credit limit is like a speed limit: the highest they can go without getting into trouble.

Credit scores place a big emphasis on how much of your credit you use every month. Called a credit utilization ratio, your score dips when that quotient climbs.

And your credit score doesn't distinguish between the balances you're paying off every month and those you don't. It only looks at the totals you're charging.

The bottom line for consumers is that if you want to keep your scores high, you need to keep those balances low .

How low can you go?

Want to calculate your utilization rate? Add up last month's card balances. Divide that by the total of all your credit limits on open credit card accounts. The two-digit number after the decimal point is your utilization rate.

Go back and do the same thing for each individual card, too. That's because the FICO score looks at how much of your total limit you're

using with all your cards together, along with each card individually, says Barry Paperno, consumer operations manager for FICO, the Minneapolis company that produces the FICO score. Utilization rates count for almost 30 percent of your score, he says.

So just how low do those rates need to be? "It varies from consumer to consumer, depending on their overall profile," says Paperno.

"The lower that percentage, the better for your score," he says. The goal is not zero, but as close to that as you can manage.

"The people in this country that have the highest scores -- 760 and above -- have an average utilization of 7 percent," says John Ulzheimer, president of consumer education for Credit.com in San Francisco. He recommends keeping those balances to 10 percent or less of the credit limit.

And that's "reasonable," says Paperno. "If you're in that range, you're not going to get yourself in a lot of trouble, score-wise," he says.

One irony for consumers is that a zero balance can hurt your score. That's because the score rewards the individual who can use credit cards but keep the balances low, says Paperno. "But zero indicates that you are not using your cards," he says.